This invention relates generally to the control of an automotive transmission or the like. More particularly, it relates to improved shift control apparatus for a multiple speed, sliding gear manual transmission.
In recent years there have been many improvements in automotive drive trains, including improvements relating to control apparatus for shifting manual transmissions. Generally, for transmissions incorporating five forward speed ratios and a reverse speed ratio, the shift control apparatus provides three crossover positions for the shift stick. Each crossover position selects an appropriate shift fork, which may be moved longitudinally to engage either of two speed ratios. Of the three crossover positions, the first selects the first and second forward speed ratios, the second selects the third and fourth forward speed ratios, and the third selects the fifth forward and reverse speed ratios. Because longitudinal movement of the same shift fork in opposite directions engages either fifth or reverse, it is possible that reverse may be engaged inadvertently during the five-four downshift.
Copending U.S. application Ser. No. 968,058 filed Dec. 11, 1978 discloses shift control apparatus wherein a main shift rail is rotatable about its longitudinal axis to four positions for crossover selection. In each of these positions the main shift rail is slidable longitudinally along its axis so as to engage the selected speed ratio. In the first and second positions, the main shift rail is slidable to engage respectively either the first and second forward speed ratios or the third and fourth forward speed ratio. In the third and fourth positions, the main shift rail is slidable to engage respectively either the fifth forward or reverse speed ratio.
An auxiliary shift rail is slidable to engage fifth, and a reverse idler gear is slidable to engage reverse. The auxiliary shift rail and the reverse idler gear are coupled with the main shift rail by a linkage mechanism. The linkage mechanism is effective to move the auxiliary shift rail in a gear-engaging direction upon sliding of the main shift rail in one longitudinal direction when in the third crossover position, while at the same time preventing movement of the reverse idler gear. The linkage mechanism also is effective to slide the reverse idler gear in the same gear-engaging direction upon sliding of the main shift rail in the opposite, longitudinal direction when in the fourth crossover position, while at the same time preventing movement of the auxiliary shift rail.
When the reverse idler gear slides in the gear-engaging direction, it comes into meshing engagement with other gears in the reverse gear train. One of these other gears is rotatable with the transmission countershaft. In some instances it may be desirable to brake the countershaft before this meshing engagement takes place. Thus, there remains a need in the art for a simple, inexpensive countershaft braking mechanism which may be incorporated in transmission shift control apparatus of the type disclosed.